It has recently become known that polychlorinated biphenyl products (PCBs) may be hazardous to human health. In the past, PCBs were commonly used as a fire-retardant material in dielectric oil used for cooling and insulating electrical distribution transformers.
Electric utilities have been required to identify distribution transformers containing PCBs as part of an effort to eliminate these chemicals from the environment. Therefore, it has become necessary to obtain fluid samples from a large number of electrical distribution transformers.
One common electrical distribution transformer is the overhead distribution transformer, commonly referred to as a "bug." This type of distribution transformer is designed to be mounted on poles at substantial heights above the ground. Such transformers may be mounted singly for single-phase services or in groups called "banks" for three-phase services. These transformers typically range in capacity from 5 kVA to 167 kVA. Transformers of this type usually include a substantially can-shaped container which is covered by a lid and sealed with a gasket between the container and lid.
The container houses the primary and secondary windings of the transformer, which are wound about a transformer core. The coils and core are typically completely immersed in an oil having a high dielectric constant to insulate the primary and secondary windings from one another. Heat generated by the windings and core during the operation of the transformer is transferred through the oil to the container and dissipated in the surrounding air.
Presently, oil samples are obtained by removing the top of the transformer from the container, retrieving an oil sample, and replacing the lid. This procedure requires that the transformer be removed from electrical sevice so that the workmen can safely work inside of the container. When removing and replacing the lid, some of the fluid inevitably drips from the lid onto the ground. Because all unidentified transformers are treated as if they are PCB-contaminated, these spills must be cleaned up in compliance with rules promulgated by the Environmental Protection Agency. Steps which must be taken include digging up ground which has been contaminated with oil, disposing of all clothing which has become contaminated with oil, and cleaning tools, etc., which may have become contaminated.
Typically, only about ten distribution transformers of the above-described type can be sampled in a working day using a three-person work crew. A significant disadvantage of this technique is that workers are directly exposed to oil which may be contaminated. Furthermore, the transformer must be removed from service (i.e., electrical power disrupted to customers) while the transformer is being sampled. In addition, the gasket between the lid and container must be replaced. It has also been found that removing the lid of the transformer exposes the dielectric fluid to possible contamination. Testing of the transformer is often limited to periods when it is not raining or snowing.
Therefore, a need exists for a method of obtaining oil samples from distribution transformers which eliminates the disadvantages of the prior art technique.